HVAC systems provide much needed climate control in buildings. To reduce the cost and energy usage of heating, cooling, and ventilating a space in commercial buildings, it is sometime useful to add supervisory control to an existing HVAC system. The supervisory control may be used, for example, to cause the HVAC system to use more energy efficient setpoints at certain times of day or when the space is unoccupied. The supervisory control may also be used to sequence the activation of multiple HVAC units in applications where there are multiple units and it is useful to limit peak electrical loads. Among other things, supervisory controls may also be used to test the HVAC equipment by forcing it into heating, cooling, or ventilation modes, while measuring the airflow or temperature of the air entering the space.
In many cases the existing HVAC system utilizes a simple temperature sensor to determine the temperature of the space. There are several common types of temperature sensors used including, but not limited to, devices whose: resistance varies with temperature, regardless of voltage and current; voltage varies with temperature, independent of current; and, current varies with temperature, independent of voltage.
In many applications existing HVAC systems do not provide an interface to communicate with a supervisory control system, so the existing HVAC system has to be replaced and/or reprogrammed in order to gain the benefits of supervisory control. Unfortunately, modification of a controller of the HVAC system to add such supervisory control requires a certain skill level, knowledge of building specifics, and/or knowledge of the particular HVAC system. Such skill level and knowledge comes at a significant financial cost.
Thus, there is a need in the art to provide a way to provide supervisory control of an HVAC system without requiring physical change to the HVAC control system or replacement of a current HVAC control system.